Establishment Of Three-dimensional Finite Element Model Of The Dentulous Mandible And Finite Element Analysis Of Rigid Internal Fixation Of Mandibular Body Fracture

Object: Mandibular fractures are the most common injuries inmaxillofacial trauma,The use of rigid internal fixation for mandibular fractures had become progressively more popular in past thirty years.The purpose of this study was to establish a three-dimensional finite element model(3-D FEM) of dentulous mandible with better similarity for the research on stress distribution during clenching and rigid internal fixation (RIF) of mandibular fractures.The stress shielding effects were also evaluated so as to provide reference optimizing rigid internal fixation design.Methods: A young female skull with normal occlusion was adopted forCT scanned transverse section and then modern computer image processing system and the finite element software (Ansys 6.0) were used to take and analyse the data to establish the 3-D FEM of mandible.The clenching task in the intercuspal position were modeled. The regularity of stress distribution of mandibular body fracture under different conditions were then analysed during different period of bone healing. The value of stress shielding rate was used to represent the level of stress shielding effects.Result: 1) A 3D-FEM of mandible including cortical bone,cancellousbone and dentition was established, which consisted of 13,320 nodes and 59,932 elements.Then ,a 3D-FEM of rigid internal fixation for mandibular body fracture was also established, which consisted of 14,256 nodes and 63,758 elements. 2) There were higher Von-Mises stress at the neck of condyle, molar region,mental foramen region ,symphsis region and angle in the intercuspal position.In these sites,the Von-Mises stress at the neck of condyle was largest,which is 8.333Mpafor cortical bone and 15.627 Mpa for cancellous bone; 3) When single and double steel miniplates were fixed respectively,the stress shielding rate were 98.90% , 99.63% and titanium miniplate 98.65% , 99.58% respectively during the earlier period of bone healing; the stress shielding rate of single and double steel miniplates were 6.8% , 22.96% and titanium miniplate 5.12% , 20.99% respectively during the middle period of bone healing; the stress shielding rate of single and double steel miniplates were 5.73% , 14.14% and titanium miniplate 4.47% , 13.71% respectively during the later period of bone healing.Conclusion: 1) The above mentioned methods were proved to befeasible in the Establishement of 3D-FEM of the dentulous mandible and could improve the biomechanical similarity of FEM of mandible effectively. The 3D-FEM could analyse the regularity of stress distribution of madibular fracture by using internal rigid fixation . 2) There were higher Von-Mises stress at the neck of condyle, molar region,mental foramen region ,symphsis region and angle under functional status. 3) The stress shielding effects definitely existed when miniplate rigid internal fixation system was chosen to treat mandibular body fractures. Stress shielding effects in the double-plated mandible were larger than that in the single-plated mandible in all time periods.The material of plate affected stress shilding effects. Stress shielding effects in the titanium-plated mandible were lower than that in the steel-plated mandible. The position of the plate also affected stress distribution of bone transverse section. In the two method of this trial ,the clinical effects were better when two miniplate were fixed in superior border and inferior border. We suggest that two miniplate were used for mandibular body fracture.